A packet switched data network such as the Internet can be considered to comprise a mass of nodes interconnected by data paths.
In packet switched data networks such as the Internet, monitoring a data path, or in other words, estimating a condition such as available bandwidth end-to-end over a data path of the network is useful in several contexts; including Service Level Agreement (SLA) verification, network monitoring and server selection.
Mainly, there are two ways to estimate a condition such as available bandwidth, namely passive or active monitoring.
Passive monitoring of available bandwidth of an end-to-end data path requires that all of the network nodes in the network path can be accessed. However, this is typically not possible. Therefore, measuring available end-to-end bandwidth is typically done by active probing of the data path. The available bandwidth can be estimated by transmitting probe traffic, such as User Data Protocol (UDP) probe packets including a train of probe packets into the data path, and then analyzing the observed effects of cross traffic on the probe packets. Typically, large UDP probe packets having a specified inter-packet separation are transmitted. This kind of active measurement requires access to both sender and receiver hosts, in the following referred to as sender and receiver nodes, but does not require access to any intermediate node(s) in the path between the sender and receiver nodes. Conventional approaches to active probing require the transmission of probe packet traffic into the data path of interest at a rate (herein, rate is defined as inter packet separation) that is sufficient transiently to use all available bandwidth and cause congestion. If only a small number of probe packets are used, then the induced transient congestion can be absorbed by buffer queues in the nodes. Accordingly, no data packet loss is caused, but rather only a small data path delay increase of a few data packets. The desired measure of the available bandwidth is determined based on the increase in delay due to the probe packets having experienced congestion between sender and receiver node. The probe packet rate where the data path delay begins increasing corresponds to the point of congestion, and thus is indicative of the available bandwidth.
When measuring data path condition such as end-to-end available bandwidth between a sender and a receiver node of a data path in a communication network, both nodes need special software installed. Because of that, it is necessary to have access to both sender and receiver node. Typically, software must be installed or one must be able to control both nodes. This may be undesired or even impossible.